Gas laser tube having a supported cathode

ABSTRACT

A hollow metal member which holds a mirror of an optical resonator in a gas laser tube is electrically and mechanically connected with a hollow cathode by a spring. The spring is positioned either outside or on the inner surface of the hollow metal member and elastically forces one end of the cathode against the inner wall of the hollow metal member.

BACKGROUND OF THE INVENTION

This invention relates to a gas laser tube, and more particularly to astructure for holding and fixing a cathode thereof.

A gas laser tube such as helium neon gas laser tube utilizes an aluminumcold cathode. This is usually of cylindrical shape and longitudinallyoverlaps within a glass envelope a capillary discharge tube. In U.S.Pat. No. 4,311,969 , a cylindrically shaped aluminum cathode has anextending cylindrical snout receivable within a central opening of anickel-iron alloy end plate for an envelope. The end plate is designedwith a central axially extending neck section defining the centralopening. The axial length of the snout of the cathode is greater thanthe axial length of the opening in the neck section of the end plate sothat the end of the snout can be peened over the neck section to effectboth electrical contact by way of the end plate and at the same time beproperly mechanically supported.

However, the difference in thermal expansion coefficient between thealuminium and nickel-iron alloy affects the reliability for electricalconnection there-between. Temperature changes occur when an opticalresonator mirror is sealed in a mirror holder with low-melting glass, orwhen the whole laser tube is baked in an oven in order to exhaust gasfrom the envelope.

Aluminum has a thermal expansion coefficient of more than three timeshigher than that of the nickel-iron alloy. For example, the thermalexpansion coefficient of a so-called 426 alloy is 90×10⁻⁷ /C.° at30°˜380° C., while the thermal expansion coefficient of Al is 29×10⁻⁶/C.° at 0°˜600° C. When heated to a high temperature an, aluminumcathode therefore tends to expand outward, but because the end platedoes not expand as much as the cathode, an internal force is exerted onthe contact point. As aluminum is much softer than the 426 alloy, thepoint on which the force is exerted is apparently deformed in the inwarddirection compared to other locations where no force is exerted. Whenthe temperature falls from this state to the normal operatingtemperature (several tens of degrees centigrade), the cathode iscompressed remarkably toward the inside, and the alignment between thecathode and the internal surface of the end plate is degraded.

As mentioned above, the cathode fixing structure is unsatisfactory inthat thermal hysteresis weakens the alignment and electric contact ofthe cathode, and if the tube is subjected to vibrations or shocks,electric discharge is instantaneously suspended.

SUMMARY OF THE INVENTION

This invention was conceived to eliminate such problems encountered inthe prior art, and aims at providing a gas laser tube which is not proneto thermal hysteresis in the fixing structure of the cathode and has ahigh resistance against vibration and shock. In order to achieve thisobject, this invention provides a gas laser tube which comprises a firsthollow metal member retaining a first mirror at one end thereof, acathode member having one end thereof inserted into an opening on theother end of the first hollow metal member and supported therewith, anelectrically conductive spring member which electrically as well asmechanically connects the cathode member with the first hollow metalmember, a capillary discharge tube having one end arranged inside anopening formed at the other end of the cathode member, an outer housingwhich houses the discharge tube and the cathode member, and a secondhollow metal member provided on the outer housing at the other end ofthe discharge tube which supports and fixes a second mirror which formsan optical resonator together with the first mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a first embodiment of a gas laser tubeaccording to this invention;

FIG. 2 is an enlarged view of FIG. 1 showing details of section A inFIG. 1;

FIG. 3A is a plane view showing a metal member 8 according to thisinvention;

FIGS. 3B and 3C are sectional views illustrating the supporting/fixingprocess of the cathode with the metal member 8 in FIG. 3A;

FIG. 4 is a plane view of a second embodiment of the metal memberaccording to this invention;

FIG. 5 is a cross-sectional view of a third embodiment of a gas lasertube according to this invention;

FIG. 6 is an enlargement of section B of FIG. 5;

FIG. 7A is a plan view of the metal member 82 in FIG. 5;

FIG. 7B is a side view of the metal member 82 in FIG. 7A; and

FIG. 8 is a sectional view of a partion of a fourth embodiment of a gaslaser tube according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 3 illustrate a first embodiment of the presentinvention. As shown in these Figures, a pair of mirrors 11, 12 for anoptical resonator are respectively fixed and supported by hollow metalsupporting members 21, 22 which are attached to both ends of a glassbulb 7 via end plates or metal sealing dishes 31, 32. The glass bulb 7is part of an outer housing. A cylindrically shaped aluminum cathode 5is open at one end and largely closed at its other end. A metalevacuation pipe 4 is soldered on the metal dish 32 while an extendingcylindrical snout 51 of the hollow aluminum cathode 5 is fixed ontosupporting part 22 which is made of a nickel-iron alloy. A funnel-shapedportion of the cathode 5 connects the snout 51 to the cylindrical bodyof the cathode 5, which has a larger diameter than the snout 51. Acapillary discharge tube 6 is secured at one end thereof to the glassbulb 7. A metal member 8 which is a spring made of stainless steel sheetis shaped like a ring having multiple projections 10 on the internalcircumference thereof as shown in FIG. 3A and is secured to the metalsupporting member 22. Reference numeral 9 in FIG. 3C denotes a press jigwhich forces the snout 51 of the aluminum cathode 5 onto the innersurface of the metal supporting member 22.

The cathode 5 is contacted tightly with the metal supporting member 22by the following process. As shown in FIG. 3B, the snout 51 of thealuminum cathode 5 is inserted into openings of the metal member 8 andthe metal supporting member 22. The metal member 8 is attached inadvance by spot welding at the locations marked X to the metalsupporting member 22 on an end surface close to the cathode.

Then, a press jig 9 is forced in as shown in FIG. 3C, and the tip end ofthe aluminum cathode 5 is forced to deform to accommodate to the shapeof the tip of the jig 9 so as to cause the cathode 5 and an inner wallof the member 22 to contact tightly and snugly with each other.

The aluminum cathode 5 is pulled in the direction of the arrows in FIG.3C by the spring force of member 8 to tightly fit the cathode 5 againstthe supporting member at a step portion 221. As the cathode 5 is made ofaluminum is and softer than member 8, which is made of stainless steel,the projections 10 of member 8 and the aluminum cathode 5 are engagedsufficiently to prevent rotational deviation from each other. Therefore,even if subjected to thermal hysteresis, the close contact of thealuminum cathode is hardly deteriorated, and the electric connectionbetween the aluminum cathode 5 and the metal supporting member 22 ismade secure.

The metal member 8 need not have projections, and as shown in FIG. 4, itmay be an annular metal member 81 having an inner diaqmeter which issmaller than the outer diameter of the cathode end and having an innercircumference which is cut to form a number of slits or notches.

The aforementioned embodiments of this invention effectively enhance thereliability of the gas laser tube as it can maintain an electricconnection between the metal supporting members and the cathode as wellas secure the cathode thereto even after thermal changes by fitting anannular metal member having multiple projections on the innercircumference thereof with a metal supporting member attached on an endsurface closer to the cathode and fixing and supporting the aluminumcathode by means of the spring force of the projections as well as theengagement between the soft aluminum cathode and the rigid projections.

FIGS. 5 to 7 show the third embodiment of this invention. In FIGS. 5 and6 the same parts are denoted by the same reference numerals as inFIG. 1. As is obvious from FIGS. 5 and 6, a laser tube is assembled byinserting a snout 51 of an aluminum cathode 5 into a metal supportingmember 22, and after a spring 82 is inserted into member 22 from outside(from the side of the mirror) and is press-fit into a groove insidemember 22. The aluminum cathode 5 is deformed by the inserted spring 82to tightly fit in the groove 222 formed inside member 22. An outwardforce is constantly applied to the area of contact due to the springforce of the spring 82.

If the spring 82 is made of a metal having a thermal expansioncoefficient smaller than that of aluminum, e.g., spring steel, theelectric as well as mechanical contact between the aluminum cathode 5and the metal supporting member 22 can be maintained even after thermalchanges.

FIG. 8 shows a fourth embodiment of this invention and the same partsare denoted by the same reference numerals as in FIG. 1. A spring 83 ismechanically fixed in advance on an aluminum cathode 5 by, for instance,inserting a pair of pins 831 of the spring 83 into a pair of holes 55bored in a reduced end of the aluminum cathode 5. When the cathode 5 isinserted into the metal supporting 22 with the spring member fixedthereon, the spring 83 fits into a tapered groove 223 formed on theinner surface of the member 22. This embodiment is advantageous in thatthe form of the groove inside the metal supporting member 22 may besimpler.

As mentioned above, the present invention is highly effective inmaintaining the mechanical of a cathode with a metal supporting memberas well as electric connection therebetween by additionally providing aspring at one end of a cathode which tightly contacts the internalsurface of the metal supporting member so as to force the cathode towardsurface by the spring force.

The structure for fixing a cathode of a He-Ne laser tube according tothis invention is particularly advantageous in that as the cathode isconstantly pressed towarde the metal supporting members by the force ofthe spring member, the cathode will not be misaligned even aftersubjected to thermal changes in the manufacturing process of the gaslaser tubes. If the spring member 8 is made of a metal having a smallerthermal expansion coefficient than that of aluminum, such as springsteel, even if tube is deformed due to the heat, the electric as well asmechanical contact between the aluminum cathode 5 and the metalsupporting member 22 will be securely maintained and electric dischargewill not be suspended even if the tube is subjected to vibration orshock.

What is claimed is:
 1. A gas laser tube comprising a first hollow metalmember having first and second ends and having a first mirror attachedat the first end thereof, a cathode member having first and second ends,the first end of which is inserted and supported in an opening at thesecond end of said first hollow metal member, a conductive spring memberconnecting electrically as well as mechanically said first end of saidcathode member with said first hollow metal member, a capillarydischarge tube having first and second ends, the first end arranged inan opening at the second end of said cathode member, an outer housingcontaining said capillary discharge tube and said cathode member, and asecond hollow metal member having a second mirror attached thereto andprovided on said outer housing opposite the second end of said capillarydischarge tube, said second mirror being arranged to form an opticalresonator together with said first mirror.
 2. The gas laser tube asclaimed in claim 1, wherein said conductive spring member is formed likea ring, the periphery of the ring member is electrically as well asmechanically connected to the second end of said first hollow metalmember, said ring member has spring like projections on the innercircumference thereof so as to be electrically as well as mechanicallyconnected to the outer surface of said cathode member, and said cathodemember is forced at one end thereof onto the inner wall of said firsthollow metal member due to the spring force of the resilient projectionsexerted in the direction of said tube.
 3. The gas laser tube as claimedin claim 1, wherein said spring member is in the form of a funnel with acenter hole, and the outer periphery of said funnel-shaped member is cutto form plural slits so as to be compressed like a spring on the outercircumference when pressed into an opening formed at one end of saidcathode member, thereby forcing said cathode member at one end thereofonto the inner wall of said first hollow metal member with the expandingforce thereof.
 4. The gas laser tube as claimed in claim 3, wherein agroove is formed on the inner surface of said first hollow metal memberfor positioning said spring member.
 5. The gas laser tube as claimed inclaim 1, wherein said spring member is a hollow cylinderical memberhaving a first end connected electrically as well as mechanically withone end of said cathode member and a second end forced onto the innerwall of said first hollow metal member with a spring force expandingbeyond the diameter of the opening at the second end of said firsthollow metal member.
 6. The gas laser tube as claimed in claim 5,wherein a groove is formed on the inner surface of said first hollowmetal member for positioning said spring member.
 7. A gas laser tubecomprising:a housing having first and second ends, the first endincluding a hollow metal member having an inner surface; first andsecond mirrors positioned at the first and second ends of the housing toform an optical resonator; a discharge tube positioned within thehousing; a cathode positioned within the housing around at least aportion of the discharge tube, the cathode including a connectingportion disposed inside the hollow metal member; and anelectrically-conductive spring mechanically connected between thecathode and the hollow metal member.
 8. The gas laser tube as claimed inclaim 7 wherein the spring is annular, is electrically and mechanicallyconnected to the hollow metal member, and has an elastic projection onthe inner circumference thereof which is electrically and mechanicallyconnected to the outer surface of the connecting portion of the cathode,the projection being elastically deformed to exert a force on thecathode in a direction to press the connecting portion of the cathodeagainst the hollow metal member.
 9. The gas laser tube as claimed inclaim 7 wherein the spring is in the form of a funnel with a center holeand has an outer periphery in which a plurality of slits are formed, andwherein the spring is inserted into the connecting portion of thecathode and elastically presses the connecting portion outward againstthe inner surface of the hollow metal member.
 10. The gas laser tube asclaimed in claim 9, wherein the hollow metal member has a groove forpositioning the spring formed in its inner surface.
 11. The gas lasertube as claimed in claim 7 wherein the spring is a hollow cylindricalmember having a first end electrically and mechanically connected withthe connecting portion of the cathode member and a second end whichelastically engages with the inner surface of the hollow metal member.12. The gas laser tube as claimed in claim 11, wherein the hollow metalmember has a depression formed in its inner surface with which thesecond end of the spring engages.
 13. A gas laser tube comprising:ahousing having first and second ends; a first hollow metal memberdisposed at the first end of the housing and having an inner surfacewith a step formed therein; a second hollow metal member disposed at thesecond end of the housing; first and second mirrors attached to thefirst and second hollow metal members, respectively, to form an opticalresonator; a discharge tube extending inside the housing between thefirst and second hollow metal members; a hollow cathode disposed insidethe housing surrounding at least a portion of the discharge tube, thecathode including a first cylindrical portion, a second cylindricalportion coaxial with the first cylindrical portion and having a smallerdiameter than the first cylindrical portion, and a funnel portion whichconnects the first and second cylindrical portions, the secondcylindrical portion having an end which engages with the step of thefirst hollow metal member; and an electrically-conductive spring whichis secured to the first hollow metal member and is electrically andmechanically connected to the second cylindrical portion of the cathode.14. A gas laser tube as claimed in claim 13 wherein the spring comprisesa ring having a plurality of elastic projections formed on its innercircumference, the projecting being elastically deformed to exert aforce on the cathode in a direction to press the prodtruding portion ofthe end of the second cylindrical portion of the cathode against thestep in the first hollow metal member.